Heavy-media fine ore concentration



Feb. 13, 1945. w. A. HAMILTON 2,369,393

HEAVY MEDIA FINE ORE CONCENTRATION Filed oct. .29, 1942 INVENT'OR WAM 75A ,4. HAMM rQ/v ATTORNEY Patented Feb. 13, 1945 HEAVY-MEDIA FINE oaE ooNcEN'raA'rloN Walter Arlee Hamilton, Stamford, Conn., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine f Application October 29, 1942, Serial No. 463,744

2 Claims.

This invention relates to an improved method of concentration of ores.

Various processes of concentrating ores have been developed using specific gravity methods for separation. by the process which used heavy media produced by the suspension of solids of high'speoliic gravity in water for the separating process. These methods of beneficiation depending on'sink and oat procedures Yhave been of great importance in the treatment of many ores as the process is extremely cheap and the metallurgical eiiiciency is much higher than ordinary hydraulic methods. However, there are very denite limitations to the type of ore which is amenable to such separation processes as they do not separate efficiently below a certain minimum size. With many ores either the mining operation itself or subsequent crushing required for liberation of values reduces part or all of the ore to a much liner size .than can be practically handled in sink and float processes -using heavy media. This is notably true in the beneflciation of various low-grade iron ores.

The' economics of iron ore beneciation is strongly iniiuenced by the fact that the iinal product commands a lowunit price, and hence costs of beneciation must be kept very low in order to render the process commercially useful. For the most part iron ore crudes requiring beneilciation are concentrated to a moderate degree incomparison with other base metal concentrations. Therefore, processes in which separation is not extremely sharp can be used with iron ores and similar ores where an extreme purity of product Y is not necessary. It is with these types of ores that the present invention `is concerned and it may be considered as a modification or improvement of known procedures. In the further detailed discussion reference will be made primarily to iron ores although the present invention is not limited to such ores and is applicable to any other ores, such as for example manganese ores, where a similar problem arises.

Some of the' advantages of the sink and float procedure in heavy media have been extended to the treatment of unsized material, or rather to material which is i relatively free from large amounts of line low density material, using a modied device which is neither a pure sink and iioat procedure nor an ordinary hindered settling classifier. Such a device and method is described and claimed in the applicationof Lewis J. Erck, Serial No. 395,809,1iled May 29, 1941. According to this procedure an apparatus of the classifier type such as for example an apparatus resembling in its gross structure an Akins classifier is modiiied and operated by maintaining a high bed of dense suspended solids with only a relatively shallow stream of supernatant water. The density of this deep pool of solids is not sufliclently high to permit a true sink and iioat separation. That is to say, the true density is below that .0f light sangue Notable success has been'obtainedmaterial. The pool oi solids is maintained to la point only a little below the overflow welr of the classifier and the solids pool is worked mechanically by modications of the Akins screw.

The combined mechanical `working and up-ilow of water results in bringing coarse low density material to the surface and as the amount of water is in general larger than in many classiiier op erations, a considerable shallow stream of water runs over the surface of the pool and over the overiiow Weir. This stream carries with it the coarse low density particles which have been 'worked to the surface of the solids pool and also takes with it a considerable amount of line high density material. In consideringthe high density material the action is primarily one of classification because the overow takes substantially only line high density material. From the standpoint of the low density material the operation is one.

depending primarily onspecic gravity and mechanical working for its operation. Therefore. this second stage in the process of the Erck application is not an ordinary classification but a concentration. However, the device operates by reason of the upward flow of Water to overflow a mixture of relativelycoarse light gangue and iine high density material, the'underiiow 'being a mixture of coarse and tlne high density material. This improved process and device has achieved considerable success in the treatment of unsized ine iron ores and such a device is in-` cluded in one o f the combined steps in the process of the present invention.

Erck describes the use of his concentra'tor in a number of methods of treatment, some of. these procedures being described in the Erck applications, Serial No. 430,342, led February 11, 1942, and Serial No. 436,419, led March 27, 1942, and also in an application of Grover J. Holt, Serial No. 437,464, led April 3, 1942. Essentially these procedures are applicable to iron ores or similar ores where there is present a large amount of fine low density material. The procedures may be briefly summarized as follows:

The unsized iron ore carrying relatively large amounts of nelyldivided siliceous gangue associated with coarse quartz and both coarse and fine iron r`oreis subjected to an ordinary freesettling classification which produces an overflow of ne gangue associated with a small amount of very fine iron ore, While the underiiow concentrator produces two products, an underiioW which contains practically all of the coarse iron ore associated with a portion oi the medium ne ore, and an overiow containing substantially all of the coarse light quartz particles associated with the portion of the fine iron particles. This overflow is then vsubjected to a treatment which removes coarse quartz particles. In commercial practice it is usual to employ a screening procedure, the screen oversize being sent to waste, but if desired, with certain ores where the coarse gangue contains values liberatable at a finer grind, the oversize may be ground to a uniform ne size preliminary to a further treatment. In

veither event the line iron cre in the screen undersize is recirculated to the-first or primary classiiier. Thus it will be seen that when screening is used silica is discharged from the system at two points, both from the oversize of the separating screen and from the overiiow of the primary classifier. Where grinding is employed all of the silica is discharged as iine material in the primary classier overflow.

The procedure of the Erck and Holt applications is used in a large commercial plant on the iron ores of the Mesabi Ranges in Minnesota and is well suited for the treatment of these ores. However, when applied to a different type of iron ore, such as for .example ores mined in Alabama, Colorado and the like, the process is not as eicient. These ores are characterized by a relatively lower content of very ne silica, but they are characterized by a relatively high iron content in very fine sizes. If, therefore, the procedures of the Erck and'Holt patents are attempted on such ores serious losses in iine iron ore result. According to the present invention the disadvantage of the Erck and Holt processes on ore containing relatively small amounts of low density material and large amounts of ne high density material are overcome and, at the same time in many cases, a much simpler procedure is effected with a notable increase in output per unit of equipment, al1 important advantages in the treatment of a relatively low valued material. Essentially the present invention shares with the Erck and Holt procedures the combination of a primary classifier and an Erck concentrator, but

both overflows of the concentrator and classifier are screened and concentrated and tailings are obtained from both overows. Recirculation of the undersize from the concentrator overflow is normally not necessary, but if employed at all constitutes only a minor amount of recirculation. There is thus obtained a high degree of recovery of high density values without losses of liine high density material and particularly in through-put due to the fact that little or no material is recirculated, the` high recirculating load which is characteristic of the Erck and Holt processes being avoided. v

Essentially the present invention, may therefore, be considered as an improvement on the Erck and Holt processes which, however, is applicable to a different class of ore. The two processes have their own place in the economics of iron ore beneciation, but where the nature of the ore permits, the lowered cost and improved efliciency of the process of the present inven tion represents a real economic advantage.

The invention will be described in greater detail in conjunction with the drawing in which he figure is a diagrammatic flow sheet for two typical ores.

The flow sheet was based on procedures employed in the beneiiciation of two typical iron ores of the Alabama region, being characterized by a relatively large amount of iron values ln iine fractions and a comparatively small amount of the silica in the ne fractions, were subjected to the procedure of the present invention,'that is to say, the feed was first sent through a primary classier, which may for example be an ordinary Akins classifier operated to have a heavy overflow as compared to the primary classifiers' used in the Erck and Holt processes, followed by treatment of the underflow or rake product in an Erck concentrator, operated as described in the Erck application, Ser. No. 395,809, referred to above. The overflow of the primary classier was sized on a 35 mesh screen, the oversize representing a barren tailing and the undersize being marketable concentrate. The concentrator overflow was likewise subjected to screening, but preferably on a somewhat coarser screen such as a 28 mesh screen, the oversize rejected, and the lundersize mixed with the rake productof the concentrator and the undersize from the 35 mesh screen as finished product.

Metallurgical results appear in the following Tables 1 and 2. In explanation of these results.

fraction 1 represents the rake dischargejof the concentrator, fraction 2 the overflow of the confl centrator, and fraction 3 the overflow of the primary classier. In the portion of the table under Recapitulation the metallurgical results are given on the total marketable concentrate and the total tailing. For convenience the figures are also given on the drawing in Fig. 1. The top line in each case refers to test one and some modifications with a greater increase in the bottom line t0 'Gest tWO- TALr. I

Fine ore concentration Test N o. 1

Assays Percent distribution Product lsiceht i g Pezant Prnt Pit'scll'lt Piliclt Pliflt Fe C80 Insol. SiO: A1101 Feed 100.00 33. 40 13. 94 2o. 63 1s. 47 3. 46 100.00 100.00 100.00 100. 00 100.00 Fraction 1 24.19 a5. s1 13.01 16. 62 14. 91 3.20 25. 94 22. 57 19. 49 19. 55 22.25 +28 mesh Frac. 28.93 25.99 15.24 30.16 27.38 3.54 22.51 31.63 42.30 43. 69 29. 49 -28 mesh Frac. 2. s. 64 44. 63 10. 31 12. 34 10.36 2.88 11.55 6. 39 5.38 5.09 6. 94 +35 mesh Frac. 3... 2. 54 13. 52 23. 46 33.12 30. 63 2. 90 1.03 4. 28 4. 03 4.22 2. 02 -35 mesh Frac. 3 35. 70 36. 46 13. 72 16. 64 14.19 3.32 38. 97 35.13 2s. 30 27. 45 39. 30

RECAPITULATION lIncludes all of fraction 1, plus the minus 28 mesh from fraction 2 and the minus 35 mesh from fraction 3. 2Includes plus 28 mesh from fraction 2 and plus 35 mesh from fraction 3.

TAaLnII Fine ore concentration Test No. 2

" Assays Percent distribution Percent Product wel ht g Per P018 Para P:1`t Pirat Fe @no 14m1- Sif 4M reed 100.00 35.30 10.10 24.18 23.00 3.03 100.00 100.00 100.00 100.00 100.00 Freedom 20.44 38. 81 0. 80 21.00 20.55 s. 10 22.47 18.84 11.81 11.80 21.45 +28mesh Free 2 28.05 24.08 10.11 41.24 40.12 2.10 `10.11 23.81 39.87 40.21 10.00 -28 mesh Free 2 11.77 4s. 80 8. 30 10.48 14.80 1 4.00- 14.02 9.13 1:88 7.42 15.51 +85 mesh Free?, 5.51 10.82 15.04 40.08 40.07 1. 80` 2.03 8.00 0.95 j 10.21 3.30 -85 mesh Fresa 88.08 09.81 11.12 `10.02` 1480 3.58 43.57 40.10 24.08 1 24.80 43.24

nEcAPI'rULATION 100. 00 a5. 80 10. 10 24. 78 zi. 60 3. 03 100.00 100. 00 100.00 100.00 100.00 ei 10. 84 40. 20 10. 20 17. 12 10. 52 s. 45 80. 00 08. 1a 50. 00 49. 58 s0 20 T0111 20.10 23.40 11.09 41.80 40.80 2.00 19.84 81.87 40.02 50.42 10.80

1 Includes all of fraction 1 plus the minus 21S-mesh portion of iractionZ and the minus 35 mesh portion oi fraction 3. 2 Includes all of plus 28 mesh and all oi plus 35mesh portions of fractions 2 and 3 respectively.

It will be noted that in Test 1, 75% of the iron content of the feed is recovered as a marketable concentrate having less than 17% of silica. It is important to note that more than half of the iron recovered is present inthe overflow of the primary classifier and would be lost if the ore were subjected to the Erck and Holt processes.

In the case of the second test over 80% of the iron is recovered in a concentrate having less than 17% of silica. In this case an even larger proportion of the recovered iron is found in the primary classifier overflow.

Where there is a considerable amount of barren gangue of sizes intermediate between 28 and 35 mesh the undersize from the 28 mesh screen may be recirculated to the primary classifier `which results in the elimination of barren gangue v in this size range with some losses of metal values.

The invention has been described in greater detail in conjunction with iron ores for which the present invention is particularly suited. It should be understood, however, that the inven- Wtion is not limited to the treatment of iron ores and on the contrary is applicable to any ore the above type of distribution'of heavy density and low density materials.

In the treatment of iron ores, manganese ores and most others the Valuable product is that of high density. Ihe process, howevenis not limited to such ores and on the contrary is applicable to ores such as coal inwhich the valuable product is that of low density.

The largest fleld of practical utility lies in the treatment of ores. However, the process is in fact not concerned with the past history of the mixtures of products treated and is applicable to mixtures artificially produced, either by partial beneiication of natural ores, such as concentrates of various kinds, mixtures obtained by artificial production, and the like. The present invention lis also not limited to the process in which the only concentration is that effected by the means of classification, concentration and sizing. On the contrary any of the products may be subjected to further treatments Such as for example froth notations, tabling and the like.

eral applicabilty of the present invention and the possibility of using itin conjunction with other taining fine high density material and coarser` s ore dressing procedures is an important practical advantage which lends great flexibility to the process and which widens its field of usefulness.

The primary classifier has been `described as one of the hydraulic type and with most ores, notably with iron ores of the type specifically illustrated, hydraulic classification presents many advantages and is the preferred type of classiflcation. However, it should be understood that this primary classification is not necessarily limited in all cases to the use of hydraulic classifiers. With certain particular ores other types of classication, such as for 'example air classification and the like, may be employed wherever the particular nature of lthe ore makes such special classification procedure desirable.

We claim:

1. A method of beneficiating mixtures containing components of higher densities and components of lower densities, in which there is a relatively small amount of finely divided material of lower density and a relatively larger amount of finely divided material of higher density, which comprises subjecting the mixture to .hydraulic classification to produce an overflow product conand poor in high density material, subjecting 1 major portions of coarse low density material,

The genand subjecting the overflow to screening to produce an undersize rich in high density material and poor in low density material and an oversize rich in low density material and poor in high density material, the screening of the overflow containing coarse low density material being at a coarser mesh size than the screening of the overflow of the primary hydraulic'classifier.

2. A method of beneciating iron ore containing iron oxide and siliceous gangue, in which there is a relatively small amount of nely divided siliceous gangue and a relatively larger amount of finely divided iron oxide, which comsiflcation to produce an overflow product containing line iron oxide and coarser siliceous gangue and an underflow product containing coarse and fine iron oxide and only coarse siliceous gangue, screening lche overflow to produce an undersize rich inviron oxide and poor in siliceous gangue and an oversize rich in siliceous gangue and poor in iron oxide, subjecting the underflow to a procedure of combined specific gravity and separation and classification, whereby an overflow is produced containing coarse siliceous gangue and fine iron oxide and an underflow is produced containing coarse iron oxide and substantially free from major portions of coarse siliceous gangue, and subjecting the overflow to screening to produce an undersize rich in iron oxide and poor. in siliceous gangue and an oversize rich in siliceous gangue and poor in' iron oxide, the screening of the overflow containing coarse low density material being at a coarser mesh size thanthe screening of the overflow of 10 the primary hydraulic classier.

WALTER ARLEE HAMILTON. 

